Sony said the newly discovered problem was with its Sony Online Entertainment servers, which stored information about 24.6 million customer accounts and 12,700 credit and debit card numbers. These servers were shut down on Monday after the company learned that hackers had also gained access.

“I am deeply concerned about the egregious inadequacy of Sony’s efforts thus far to notify its customers of these breaches or to provide adequate protections for users whose personal and financial information may have been compromised,” Senator Blumenthal wrote in the letter. “Sony’s failure to adequately warn its customers about serious security risks is simply unconscionable and unacceptable.”

Last week, after near-silence from Sony, Senator Blumenthal sent a letter to Sony asking why customers had not been notified sooner about the security breach. The senator said he was particularly concerned that many of the users of the company’s PlayStation network were children. In his latest letter he said the company had not yet responded to the first.

Sony did not immediately respond to a request for comment on the letter.

Sony representatives had also been asked to testify before a Congressional committee on Tuesday, but declined, citing an ongoing investigation involving law enforcement. A Sony representative said in an e-mail message that the company “is cooperating with the request for answers to the committee’s questions, and in fact will be providing our responses in advance of the deadline.”